The present invention relates to inflatable protective cushions, and more specifically relates to airbags useful in side protection of occupants in a transportation vehicle, such as an automobile.
Inflatable protective cushions used in passenger vehicles are a component of relatively complex passive restraint systems. The main elements of these systems are: an impact sensing components, an ignition component, a propellant material or stored gas system, an attachment device, an enclosure, and an inflatable protective cushion. Upon sensing an impact, the stored gas system is ignited causing an explosive release of gases filling the cushion to a deployed state that can absorb the impact of the movement of a body against it and dissipate its energy by means of venting of the gas. The entire sequence of events occurs within about 20 milliseconds.
This inflation medium is generally nitrogen or helium gas generated from a gas generator or inflator (the term “airbag” will be used for convenience herein regardless of the inflation medium actually used). The inflation medium is conveyed into the cushion at a relatively warm temperature.
In the un-deployed state, the airbag is most commonly stored in or near the steering column, the dashboard, in a door panel, or in the back of a front seat placing the cushion in close proximity to the person or the object it is to protect.
A typical construction material for airbags has been a polyester or nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yarn by weaving practices that are well known in the art. The use of a coating material has found acceptance because it decreases the rate of permeability of the inflation medium. The coating helps to block the permeation of the fabric by such gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event.
Airbags may also be formed from uncoated fabric that has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendaring to reduce permeability. Fabrics that reduce air permeability by calendaring or other mechanical treatments after weaving are disclosed in U.S. Pat. No. 4,921,735; U.S. Pat. No. 4,977,016; and U.S. Pat. No. 5,073,418 (all incorporated herein by reference).
Silicone coatings typically utilize either solvent-based or complex, two-component reaction systems. Dry coating weights for silicone have been in the range of about 3 to 4 ounces per square yard or greater for both the front and back panels of side curtain airbags. Alternatively, the use of a particular type of polyurethane as a coating as disclosed in U.S. Pat. No. 5,110,666 to Menzel et al. (herein incorporated by reference) permits low add on weights reported to be in the range of 0.1 to 1 ounces per square yard but the material itself is relatively expensive and is believed to require relatively complex compounding and application procedures due to the nature of the coating materials.
The driver-side airbags are typically of a relatively simple configuration in that they function over a fairly small well-defined area between the driver and the steering column. One such configuration is disclosed in U.S. Pat. No. 5,533,755 to Nelsen et al., issued Jul. 9, 1996, the teachings of which are incorporated herein by reference. However, inflatable cushions for use in the protection of passengers against frontal or side impacts must generally have a more complex configuration since the position of a vehicle passenger may not be well defined and greater distance may exist between the passenger and the surface of the vehicle against which that passenger might be thrown in the event of a collision.
The majority of commercially used restraint cushions are formed of woven fabric materials utilizing multifilament synthetic yarns of materials such as polyester, nylon 6 or nylon 6,6 polymers.
As will be appreciated, the permeability of the cushion structure is an important factor in determining the rate of inflation and subsequent rapid deflation following the impact event. In order to control the overall permeability of the cushion, it may be desirable to use differing materials in different regions of the cushion. Thus, the use of several fabric panels in construction of the cushion may prove to be a useful design feature. The use of multiple fabric panels in the cushion structure also permits the development of relatively complex three-dimensional geometries that may be of benefit in the formation of cushions for passenger side applications wherein a full bodied cushion is desired. While the use of multiple fabric panels provides several advantages in terms of permeability manipulation and geometric design, the use of multiple fabric panels for use in passenger side restraint cushions has historically required the assembly of panels having multiple different geometries involving multiple curved seams.
As will be appreciated, an important consideration in cutting panel structures from a base material is the ability to maximize the number of panels which can be cut from a fixed area through close-packed nesting of the panels. It has been found that minimizing the number of different geometries making up panels in the cushion and using geometries with substantially straight line perimeter configurations generally permits an enhanced number of panels to be cut from the base material. The use of panels having generally straight-line profiles has the added benefit of permitting the panels to be attached to one another using substantially straight seams or to be substantially formed during the weaving process using a jacquard or dobby loom. For the purposes of this invention, the term “seam” is to be understood as any point of attachment between different fabric panels or different portions of the same fabric panel. Thus, a seam may be sewn (such as with thread), welded (such as by ultrasonic stitching), woven (such as on a jacquard or dobby loom, as merely examples), and the like. The key issue regarding seam length within this invention pertains to the ability to form a highly available inflation airspace volume cushion with the lowest amount of labor needed. Since sewing, welding, etc., procedures to connect panels or portions of panels greatly increases the time necessary to produce airbag cushions, it is highly desirable to reduce the labor time which can be accomplished through the reduction in the length of seams required. Substantially straight seam configurations thus provide more cost-effective methods of producing such airbags.
As alluded to above, in addition to driver-side and passenger-side airbags, there are side impact and side curtain airbags. Side impact airbags are linear, tubular structures; side curtain airbags are panel-like and cover a larger area. These both have been designed primarily to protect passengers during side crashes and to provide rollover protection, unfolding from packing housings stored within the roofline along the side windows of an automobile (and thus have a back and front side only). Side curtain airbags not only provide cushioning effects but also provide protection from broken glass and other debris. As such, it is imperative that side curtain airbags, as noted above, retain large amounts of gas, as well as high gas pressures, to remain inflated throughout the longer time periods of the entire potential rollover situation. To accomplish this, these side curtains are generally coated with very large amounts of sealing materials on both the front and back. Since most side curtain airbag fabrics comprise woven blanks that are either sewn, sealed, or integrally woven together, discrete areas of potentially high leakage of gas are prevalent, particularly at and around the seams.
In addition to the duration of air retention, side impact airbags and side curtain airbags must be able to contract upon inflation to achieve a high degree of tension against the lateral force of the occupants of the vehicle. Ideally, this tension should be as high as possible, and be sufficiently high with relatively low volumes of air in the airbag so that, even while still inflating, they provide restraint against lateral forces.